Had it been me, he'd still be there waiting. Every time this happens, I pass them on the left, just as I'm supposed to do. I won't pick up a stranger's invitation to break the rules. I figure they need the insurance money and think they've spotted a sap to let them cash-in.
I would have passed on the left, but he had moved all the way over to the left (before making a right!), so I couldn't go around without crossing into oncoming traffic. When he first waved me on, I shook my head and waved for him to go, but he was insistent. I didn't want to hold up traffic, so I went ahead on his right. I'm still not entirely clear about how I could have handled it better, but you've given me something to think about.